Heterorhabditis bacteriophora
Grub nematode (Hb)- Rate
- 250k–500k /m²
- Temp
- 12–35 °C soil (sources vary)
- Best for
- Grubs in the lawn, August to early September
Pest
Japanese beetle
Popillia japonica
The short answer
A metallic green beetle with copper-brown wing covers, about 11 mm long, that feeds in groups on the leaves, flowers and fruit of more than 300 plants. Roses, grapes and lindens are among its favourites. It eats the leaf between the veins and leaves a lace-like skeleton. The quickest control in a garden is to shake the beetles into a bucket of soapy water early in the morning. Pheromone traps are not worth using, because in University of Kentucky trials they drew in more beetles than they caught and plants near the traps lost more leaves. The larva is a C-shaped white grub that feeds on grass roots from late summer.
hero macro · adults feeding on a rose leaf
Adult Popillia japonica on a skeletonised rose leaf. Photo: pending.
Identification
Adults are 1/3–1/2 inch (about 8–13 mm) long, with a metallic green head and thorax and copper-brown wing covers. The surest tell is the white hair: University of Minnesota counts five white patches along each side of the abdomen and two more at the tip. They fly by day and feed in groups, usually starting at the top of the plant. The damage draws in more beetles, because the smell of leaves that other beetles have already damaged appears to draw them in.
The grub is the larva. It is C-shaped and creamy white with a tan head, and reaches about 1 inch (2.5 cm) by late August. You cannot tell it from other lawn grubs by size. Look through a hand lens at the underside of the last segment, called the raster: Japanese beetle grubs have spines in a V-shaped pattern, while masked chafer grubs have a scattered pattern and a darker chestnut head. See white grubs for the full set.
Easily confused with
- Rose chaferAlso a pestAlso on roses and grapes, but tan to pale green all over with long, spiny orange-brown legs, and no metallic green head. In the Northeast it appears a few weeks before Japanese beetles.
- Green June beetleAlso a pestMetallic green too, and its leaf damage looks similar, but it is nearly 1 inch long with bronze to yellow edges. A Japanese beetle is 1/3–1/2 inch with copper-brown wing covers and white hair tufts on its sides.
- Other lawn grubsAlso a pestMasked chafer and other grubs look the same by size. Under a hand lens, a Japanese beetle grub has a V-shaped pattern of spines under its tail; a masked chafer's is scattered, with a darker chestnut head.
Damage symptoms
The adults and the grubs damage different plants. Adults chew leaves, flowers and overripe or wounded fruit, and feed in groups, so a plant can be stripped from the top down while its neighbour is barely touched. Their damage looks worse than it usually is: in a Virginia study, defoliation of grapevines by natural beetle populations did not significantly reduce fruit quality, yield or shoot growth. No damage threshold has been set for woody landscape plants. The grubs feed on grass roots from late summer, and in large numbers they kill patches of lawn.
- Leaves eaten between the veins until only a lace-like skeleton is left
- Groups of green beetles feeding from the top of the plant down
- Rose buds and open flowers chewed ragged
- Overripe or damaged fruit hollowed out
- In the lawn: patches of turf that pull up like a loose carpet, with C-shaped grubs under the roots
Lifecycle & degree days
One generation a year across most of its range in the United States. In cooler northern areas, including southern Ontario, northern New England and parts of New York, some of the population takes two years. Adults come out of the soil from late spring to midsummer, depending on latitude. Females alternate between feeding on plants and going back into the soil to lay eggs. The grubs feed on roots through the autumn, move deeper to spend the winter, and come back up to feed in spring before they pupate. In Europe it is a priority pest for the EU: it was found in northern Italy in 2014 and by 2022 the outbreak covered more than 16,000 km² of northern Italy and southern Switzerland.
- Generations
- 1 a year; some take 2 years in the cool north
- Adults emerge
- May (S. Georgia), June (Kentucky), July (E. Massachusetts)
- Eggs per female
- 40–60, laid over a 4–6 week adult life
- Egg to 3rd-instar grub
- Hatch in 10–14 days; most grubs are 3rd instar by mid-September
- Overwinters
- As grubs, mostly 5–15 cm below the surface; a few go 20–25 cm deep
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Host crops
Adults feed on more than 300 kinds of plant, but they have strong favourites. Kentucky Extension names roses, grapes, lindens, sassafras, Norway and Japanese maples and purple-leaf plum as especially prone to damage, and lists apples and flowering crabapples among the plants likely to be attacked. Minnesota adds raspberries and basil. The grubs feed on grass roots, so the same garden often has damaged roses in July and a damaged lawn in September.
Monitoring & action thresholds
Action threshold
About 10 grubs per ft²
This applies to the grubs in turf. Sources differ: UMass gives 8–15 Japanese beetle grubs per ft², Purdue 10 or more, and the Northeastern IPM Center 6–12 in unirrigated turf. Irrigated turf tolerates more. No threshold has been set for adult feeding on landscape plants.
For adults, check the plants you know they like from late spring. Traps are for detection, not control: in Kentucky trials on a golf course and in home landscapes, plants with a trap nearby nearly always lost more leaves than plants without one, and a plant ringed by three traps was more than 90% defoliated within 30 hours. State survey programmes use traps to find new infestations. For grubs, wait until August or early September. Cut out one square foot of turf in several places, turn it back, and count the grubs in the roots and the top 2–4 inches (5–10 cm) of soil. Healthy turf outgrows a few grubs, so only the count tells you whether to treat.
Beneficial
Biological control
No natural enemy gives reliable control of the adults. A biological spray is the exception that helps: in Kentucky trials, Bt galleriae (beetleGONE!) residues cut feeding on roses and lindens for 3–14 days, and Minnesota Extension rates it moderately effective for one to two weeks, though most beetles that fed on treated leaves could still fly a day later. Keep it off milkweed: it killed 97–100% of young monarch caterpillars. For the grubs, the insect-killing nematode Heterorhabditis bacteriophora is the biological option with field evidence, although results are inconsistent. Several parasitoids introduced from Asia are established in the United States: Tiphia vernalis, a wasp that parasitises overwintered grubs in spring; Tiphia popilliavora, which attacks young grubs in late summer; and Istocheta aldrichi, a tachinid fly that parasitises newly emerged adults. Minnesota recently recorded 16–30% of adults parasitised by Istocheta. They occur too sporadically to rely on. Ants, rove beetles and ground beetles eat many eggs and young grubs. Milky spore is sold for this beetle, but the evidence for it is poor.
Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Background predation on eggs and young grubs
Staphylinidae
Rove beetles- Kind
- Wild — attract it
- Best for
- Background predation on eggs and young grubs
Bacillus thuringiensis subsp. galleriae strain SDS-502
Bt galleriae (Btg)- Rate
- Maker's rate — beetleGONE! 2–4 oz per gallon of water, sprayed on foliage where beetles feed every 7–10 days; grubGONE! 3 lb per 1,000 sq ft, watered in
- Best for
- Leaf spray; cuts adult feeding for 3–14 days, doesn't kill fast
Cultural controls
Kentucky Extension calls shaking the beetles off early in the morning, while they are sluggish, one of the easiest ways to clear small plants. Minnesota Extension lists the lower-risk sprays as pyrethrins and neem, and chlorantraniliprole as a residual option with low risk to bees. Pyrethroids, carbaryl, acephate and the systemic neonicotinoids all harm pollinators.
- Shake or knock the beetles into a bucket of soapy water early in the morning or in the evening, while they are cool and slow
- Keep checking and removing them through the flight — beetles tend to gather on plants where others have already fed
- Cover roses and other valued plants with cheesecloth or fine netting at peak beetle activity
- Do not use Japanese beetle traps near plants you want to protect — they attract more beetles than they catch
- Where beetles are a yearly problem, plant ones they seldom damage, such as boxwood, flowering dogwood, hollies, magnolias and white, red and scarlet oaks
- Do not treat the lawn to protect the roses — adults fly in from a distance, so grub control does not stop adult feeding
Chemical, last resort
Never spray plants in flower — carbaryl, the pyrethroids and the neonicotinoids are all toxic to beesCheck any product before it goes on. Open the compatibility matrix →
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Potter & Held, Biology and Management of the Japanese Beetle, Annu. Rev. Entomol. 47:175–205 (2002)
Gordon & Potter, Efficiency of Japanese beetle traps…, J. Econ. Entomol. 78:774–778 (1985)
Univ. of Kentucky ENTFACT-451, Japanese Beetles in the Urban Landscape (Potter et al., rev. 2026)
Univ. of Kentucky ENT-10, Controlling White Grubs in Turfgrass (M.F. & D.A. Potter, 1999)
Univ. of Minnesota Extension, Japanese beetles in yards and gardens (Hahn et al., reviewed 2025)
Penn State Extension, White Grubs in Home Lawns (Heller, updated 2026)
Purdue Extension E-271, Managing White Grubs in Turfgrass (Richmond, 2023)
UMass Extension, Turf BMPs Section 11: Insect Management (threshold table)
Northeastern IPM Center, White Grubs (school IPM best practices)
Gotta et al., Popillia japonica — Italian outbreak management, Front. Insect Sci. 3 (2023)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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